How the packet travels?

Richard Corfield Richard@littondale.freeserve.co.uk
Tue, 28 Sep 1999 09:29:05 +0100 (BST)


On Tue, 28 Sep 1999, Kins Orekhov wrote:

> and IPtables Howto says very different
> 
>                     _____
>                    /     \
>  -->[Routing ]--->|FORWARD|------->
>     [Decision]     \_____/        ^ 
>          |                        |
>          v                       ____  
>         ___                     /    \ 
>        /   \                   |OUTPUT|
>       |INPUT|                   \____/ 
>        \___/                      ^    
>          |                        |
>          ----> Local Process ----
> 
> 

This looks very sensible and far more flexible. The diagram can be
considered as a triangle with 3 places at its 3 points: 

  A source of incoming packets

  Local Processes

  A sink for outgoing packets

The possible routes between these 3 points can be considered as the 3
lines of the triangle which is what you have drawn. The routing decision
is needed so that the kernel can decide which side of the triangle
incoming packets should go down. 

This solution gives the ability to individually control any of the three
paths, wheras before all forwarded packets also passed through "input" 
and "output" so it was impossible, or more difficult, to forward something
that would be blocked by any of the other two rules. 

HTH

 - Richard.

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